The present invention relates to voice coils used to actuate a head arm assembly in a hard disk drive.
Hard disk drives typically have a head arm assembly which rotates about a pivot axis to extend multiple heads to a stack of disks. The stack of disks are spun about a spindle between the heads. The rotation of the head arm assembly to extend the heads into the disk area is typically done using a voice coil and permanent magnets. The voice coil is a flat loop containing numerous windings of a wire. The voice coil is connected to the head arm assembly and is located between permanent magnets which are mounted above and below the voice coil and connected to the disk drive housing. When a current is forced through the wires of the voice coil, a magnetic field is generated which interacts with the magnetic field of the magnets to cause a force to be exerted on the voice coil. This force causes the voice coil to move, thereby causing the head arm assembly to rotate around its pivot axis.
The voice coil is coupled to the head arm assembly, rather than the permanent magnets being coupled to the head arm assembly, because such a voice coil typically has less weight than the permanent magnets. The smaller weight reduces the inertia of the head arm assembly, thus requiring less force to rotate it. As disk drives have become smaller and smaller, it has become more important to miniaturize components, resulting in a number of tradeoffs. For instance, the force exerted by the voice coil is proportional to the number of turns of the coil. However, a larger number of turns not only adds to the inertia of the head arm assembly, also requires more space for the voice coil. It is possible to get the same force with a smaller voice coil by using a higher quality permanent magnet, such as a neodymium type magnet rather than ceramic magnetic. Such a neodymium type magnet will produce a stronger magnetic force.